Devices, systems, and methods for carbonation of deionized water

ABSTRACT

Devices, systems, and methods employed in wet cleaning semiconductor devices are provided. In particular, systems that can deliver deionized water with the desired concentration of CO2 and methods of generating deionized water with a desired concentration of CO2 for use in wet cleaning of semiconductor devices are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/873,776, filed Oct. 17, 2007, now U.S. Pat. No. 7,731,161, whichclaims the benefit of and priority to U.S. Provisional PatentApplication Ser. No. 60/852,265 filed on Oct. 17, 2006, the entireteachings of which are incorporated herein by reference.

FIELD OF THE INVENTION

In general, the invention relates to devices, systems, and methodsemployed in wet cleaning semiconductor devices. In particular, theinvention relates to systems that can deliver deionized water with thedesired concentration of CO2 and methods of generating deionized waterwith a desired concentration of CO2 for use in wet cleaning ofsemiconductor devices.

BACKGROUND OF THE INVENTION

Microelectronics chips such as integrated circuits are made fromcomparatively large wafers of semiconductor material. This processtypically involves multiple successive steps including the following:generation of an etch mask photolitographically; etching of a layer ofmaterial as defined by the mask; removal of the photolithographic maskthrough some combination of wet and dry chemical techniques; anddeposition of layers of materials. The photolithographic mask is formedfrom a polymeric material called a photoresist. After the photoresistmask has been removed, a final cleaning step, called rinsing or wetcleaning, is typically performed.

Deionized (DI) water is known for its use in this rinsing ofsemiconductor devices. It is known to prevent any metal corrosion andcontamination of the devices. In order to make the wet cleaning moreeffective, gases such as carbon dioxide (CO2) and nitrogen (N2) haveoften been mixed with the DI water. Rinsing with carbonated deionized(DI-CO2) water is an electrically inert process that allows for damagefree cleaning while maintaining the device integrity.

Carbonated deionized (DI-CO2) water can be created by inserting carbondioxide (CO2) and water (H2O) or deionized (DI) water into a contactor.The contactor allows for the carbon dioxide (CO2) and the water (H2O) todirectly contact one another without dispersing one phase into theother. There exists various types of contactors. For example, membranecontactors allow for a “bubble free” carbonated deionized (DI-CO2) waterbut cause a low CO2 mass transfer efficiency due to diffusion rates ofCO2 through the membrane located therein. In addition, the membrane ofthe membrane contactor has a limited lifetime and requires regularmaintenance. Another example of a contactor is a packed column typecontactor. Packed columns typically have a high mass transferefficiency, however the packed column presents several disadvantages.For example, the high mass transfer efficiency requires that the packedcolumn is filled mostly with CO2 while H2O rinses over a high surfacearea of the packed column's tower packing. Flowing CO2 gas through acontinuous H2O phase is inefficient because the bulk of the H2O providesa high diffusion resistance compared to the thin water film rinsing downthe tower packing. Thus the diffusion rate of the CO2 into the H2O islimited. Further, a continuous H2O phase can require extraneous andexpensive measurement devices to control a level of H2O in the packedcolumn because if the H2O level becomes too high, the CO2 gas flowsmostly through the H2O resulting in a less efficient operation. Also, acontinuous H2O phase can require controlling of the level of H2O toavoid CO2 in the H2O outlet and H2O in the CO2 outlet. Furtherdisadvantages of the packed column are as follows: 1) CO2 is lost at theoutlet of an inert gas that is typically used in the packed column, 2)the injection of the inert gas can lower the CO2 concentration, thuslowering the overall mass transfer efficiency.

Controlling the proportions of these gases require considerably complexinstrumentation and high costs which are significant disadvantages ofcurrent methods. Typically, an excess of gas is used which can lead totoxicity and disposal problems with respect to the unused gasesparticularly carbon dioxide. As a result, these processes are expensiveand cumbersome.

SUMMARY OF THE INVENTION

In one aspect, the invention features a system for carbonation ofdeionized water. The system includes a deionized water source, a carbondioxide gas source and a contactor in fluid communication with thedeionized water source and the carbon dioxide gas source via at leastone inlet of the contactor, to generate carbonated deionized water. Thesystem also includes at least one sensor in fluid communication with theat least one inlet or at least one outlet of the contactor for measuringflow rate of the deionized water and temperature of the deionized water.The system also includes a controller in communication with the at leastone sensor and the carbon dioxide gas source for determining an amountof carbon dioxide gas the carbon dioxide gas source supplies to thecontactor such that a specific conductivity of the carbonated deionizedwater is generated in the contactor, wherein the determination is basedon the measured flow rate and temperature.

In some embodiments, the system includes one or more flow restrictorsand one or more valves that are in fluid communication with the carbondioxide gas source and the contactor for controlling the amount and flowrate of carbon dioxide gas entering the contactor. In some embodiments,the controller varies the at least one valve between an open and aclosed position such that an average amount of carbon dioxide gas thatflows from the carbon dioxide gas source to the contactor issubstantially equal to the determined amount of carbon dioxide gassupplied by the carbon dioxide gas source.

In some embodiments, the system includes at least four flow restrictors.In some embodiments the system includes an outlet of the contactor forpurging an amount of carbon dioxide gas. In some embodiments, thecontroller determines the amount of carbon dioxide gas to purge suchthat a specific conductivity of the carbonated deionized water isgenerated in the contactor.

In some embodiments, the system includes at least one flow restrictor influid communication with the outlet of the contactor and a drain forcontrolling the amount and flow rate of carbon dioxide gas purged fromthe contactor. In some embodiments, the system includes at least oneflow orifice in fluid communication with the outlet of the contactor anda drain for controlling the amount and flow rate of carbon dioxide gaspurged from the contactor.

In some embodiments, the controller sets a pressure of carbon dioxidegas at the at least one inlet. In some embodiments, the deionized waterprovided by the deionized water source and carbon dioxide provided bythe carbon dioxide source are mixed prior to entering the contactor.

In some embodiments, the system includes a first sensor in fluidcommunication with at least one inlet of the contactor for measuringflow rate of the deionized water and a second sensor in fluidcommunication with at least one outlet of the contactor for measuringtemperature of the deionized water.

In some embodiments, the system includes a first sensor in fluidcommunication with at least one inlet of the contactor for measuringtemperature of the deionized water and a second sensor in fluidcommunication with at least one outlet of the contactor for measuringflow rate of the deionized water.

In another aspect, the invention involves a method for carbonation ofdeionized water. The method involves supplying deionized water to acontactor, supplying carbon dioxide gas to the contactor and measuring,with at least one sensor, flow rate of the deionized water andtemperature of the deionized water, wherein the at least one sensor ispositioned at an inlet of the contactor or an outlet of the contactor.The method also involves, determining an amount of carbon dioxide gas tosupply to the contactor such that a specific conductivity of carbonizeddeionized water is generated by the contactor in communication with theat least one sensor and the supply of carbon dioxide gas, wherein thedetermination is based on the measured flow rate and temperature. Themethod also involves, supplying the determined amount of carbon dioxideto the contactor via one or more flow restrictors and one or more valvesthat are in fluid communication with the supply of carbon dioxide gasand the contactor and flowing the carbonated deionized water of aspecific conductivity from the contactor.

In some embodiments, the method involves varying the at least one valvebetween an open and a closed position such that an average amount ofcarbon dioxide gas that flows from the carbon dioxide gas source to thecontactor is substantially equal to the determined amount of carbondioxide gas supplied by the carbon dioxide gas source. In someembodiments, the method involves purging an amount of the carbon dioxidegas through an outlet of the contactor. In some embodiments, the methodinvolves determining the amount of carbon dioxide gas to purge such thata specific conductivity of the carbonated deionized water is generatedin the contactor.

In some embodiments, the method involves at least one flow restrictor influid communication with the outlet of the contactor and a drain forcontrolling the amount and flow rate of carbon dioxide gas purged fromthe contactor. In some embodiments, the method involves at least oneflow orifice in fluid communication with the outlet of the contactor anda drain for controlling the amount and flow rate of carbon dioxide gaspurged from the contactor. In some embodiments, the method involvessetting a pressure of carbon dioxide gas at the at least one inlet. Insome embodiments, the method involves mixing deionized water provided bythe deionized water source and carbon dioxide provided by the carbondioxide source prior to entering the contactor.

In some embodiments, the method involves measuring flow rate, with afirst sensor, of the deionized water at an inlet of the contactor andmeasuring temperature, with a second sensor, of the deionized water atan outlet of the contactor.

In some embodiments, the method involves measuring temperature, with afirst sensor, of the deionized water at an inlet of the contactor andmeasuring flow rate, with a second sensor, of the deionized water at anoutlet of the contactor.

The systems and methods of the present invention provide a number ofadvantages. One advantage of the present invention is that theconductivity as provided by the systems and methods can change veryquickly in response to a change in the conductivity set point. Inaddition, the system of the present invention does not require an inertgas, thus the outlet typically is used to purge excessive CO2 in case ofa lowering of the conductivity set point or to purge inert gas that haveenriched from the H2O in the CO2-gas in the contactor.

Another advantage of embodiments of the present invention is that flowrestrictors control the CO2 flow and the DI water flow. This isadvantageous for several reasons. First, flow restrictors are smaller insize than Mass Flow Controllers (MFC's) allowing the system to be morecompact. Second, flow restrictors are typically less expensive thanMFC's. Third, flow restrictors are available in materials that arecompatible with carbonated deionized water. Thus, providing theadvantage that the flow restrictor is not damaged by unintended contactwith CO2, as is the case with an MFC. Fourth, safety measure taken toavoid back flow into the MFC's are not necessary with flow restrictorsbecause back flow is not likely with flow restrictors. As a result,these safety measures can be eliminated or reduced, thereby decreasingcosts and/or increasing efficiency.

BRIEF DESCRIPTION OF DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 is a block diagram of a first embodiment of the system forgenerating DI-CO2 water.

FIG. 2 is a block diagram of a second embodiment of the system forgenerating DI-CO2 water.

FIG. 3 is a block diagram of a third embodiment of the system forgenerating DI-CO2 water.

FIG. 4 is a detailed block diagram of an embodiment of the system forgenerating DI-CO2 water.

FIG. 5 is a detailed block diagram of another embodiment of the systemfor generating DI-CO2 water.

FIG. 6 is a detailed block diagram of yet another embodiment of thesystem for generating DI-CO2 water.

FIG. 7 is a cross-section of an embodiment of the contactor.

FIG. 8 is a graph showing the solubility of CO2 gas in DI water atdifferent values of temperature and pressure.

FIG. 9 is a graph of the dosage of CO2 gas per liter of DI water versusthe conductivity of the DI-CO2 water.

FIG. 10 is a graph of the conductivity of the DI-CO2 water versus thetemperature.

FIG. 11 is a detailed block diagram of an embodiment of the system forgenerating DI-CO2 water.

FIG. 12 is a flow diagram of an embodiment of a method for generatingDI-CO2 water.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides devices, systems, and methods of makingDI-CO2 water for wet cleaning of semiconductor devices. In general, thedevices, systems, and methods provide wet cleaning of semiconductordevices while preventing or reducing damage created by electrostaticcharge. In one aspect, the invention provides a device with a high levelof control and consistency over a desired concentration of carbondioxide in the DI-CO2 water. In another aspect, the devices, systems andmethods can be used to generate DI-CO2 water containing a large range ofdifferent CO2 concentrations. For example, the devices, systems andmethods can generate low CO2 concentration DI-CO2 water (0.154 mg/L CO2)as well as high CO2 concentration DI-CO2 water (1540 mg/L). In general,the devices, systems, and methods of the present invention eliminate aneed for adding excess CO2 gas, nitrogen gas, or any other gas to acontactor for the DI-CO2 generation, thereby reducing the cost, size andcomplexity of the devices, systems, and methods. Most, if not all, ofthe carbon dioxide gas utilized in the devices, systems, and methodsgets dissolved in the DI water. As a result, disposal and toxicityissues are reduced over conventional systems which typically use excessCO2 gas.

In certain embodiments, the invention provides devices, systems andmethods of making DI-CO2 water in which conductivity of the DI-CO2 watercan be efficiently controlled and altered quickly during manufacture. Inanother aspect, the devices, systems and methods of the presentinvention use flow restrictors which do not need to be monitored forflow back of water, thus eliminating the need for additional safetymonitors. Flow restrictors and valves are also compatible with DI-CO2,minimizing the risk of corrosion in the system. As a result, the overallcost, size and required maintenance of the system is reduced.

FIG. 1 shows an embodiment of a system used to carbonate ultra-pure DIwater (i.e., add CO2 to the DI water). System 101 typically includes asource of electrical power supply 105, a gas module 110, a contactor115, and a sensor module 120. System 101 can also include a controlmodule 125.

The gas module 110 can be connected to one or more sources of gases suchas CO2 and Nitrogen. Gas module 110 can include a plurality of variablevalves, on/off valves, filters and mass flow controllers to monitorand/or control the flow rate and amount of each gas entering and exitingthe gas module 110. The gases can exit the gas module 110 separately orcan be pre-mixed before exiting. Upon exiting the gas module 110, thegases can be delivered to contactor 115.

Contactor 115 typically includes at least one inlet for the gases, atleast one inlet for DI water, at least one outlet to release excess gasand at least one outlet to release DI-CO2 water. The gases can beinjected, or purged into the contactor 115. The contactor 115 can bepressurized or evacuated if desired. The contactor 115 typically allowsfor generation of bubble free DI-CO2 water.

The DI-CO2 water can be released from contactor 115 and passed throughsensor module 120. Sensor module 120 can include a plurality of sensorsto monitor and/or control a plurality of parameters of the DI-CO2 water.Such parameters can include flow-rate, conductivity, temperature andpressure of the DI-CO2 water. The DI-CO2 water can be drained out of thesensor module 120 to be used as required or can be redirected back intothe system if necessary.

System 101 can include a control module 125 in fluid communication withsensor module 120 and gas module 110. Control module 125 can include aprocessor, a keypad and a display. The processor can be for example, amicroprocessor of a computer. Control module 125 can allow automaticcontrol and/or monitoring of each valve, mass flow controller and sensorin system 101. Each valve, mass flow controller and sensor in system 101can also be controlled manually.

In one embodiment, the control module 125 can determine an amount of CO2to provide to the contactor 115 based upon a conductivity (L) set-pointcontrolled by a user. For example, when CO2 is dissolved in H2O, itforms carbonic acid (H2CO3) according to the following reaction:CO2(aq)+H2O<−>H2CO3  EQN. 1

where CO2(aq) refers to dissolved CO2. At room temperature,approximately 0.3% of the CO2(aq) converts to H2CO3. A species (H2CO3*)can be defined as follows:[H2CO3*]=[CO2(aq)]+[H2CO3]  EQN. 2

The concentration of CO2(aq) is proportional to the concentration ofH2CO3*. In some embodiments, the CO2(aq) is proportional to the H2CO3*within an accuracy limit of 1%.

To obtain the CO2(aq) as a function of the conductivity (L), theequation for the dissociation constant (K1) of the H2CO3 andconductivity (L) of the CO2(aq) can be used. Using the relationship inEQN. 2, a dissociation constant (K1) of H2CO3 can be defined as follows:K1=[H+][HCO3−]/[CO2(aq)]  EQN. 3where H+ is a Hydrogen ion and HCO3− is a Bicarbonate ion.

The conductivity (L) of the CO2(aq) is proportional to the concentrationof [H+] and [HCO3−] according to the following:L=A*[H+]+B*[HCO3−]  EQN. 4where A is the specific molare conductivity for the hydrogen ion [H+}and B is the specific molare conductivity of the bicarbonate ion.

Typically, the CO2 is dissolved in deionized water (DI). In theseembodiments, the concentrations of H+ and HCO3− are equal. In theseembodiments, EQN. 3 and EQN. 5 are reduced to the following:[CO2(aq)]=[HCO3−]²/K1  EQN. 5L=(A+B)*[HCO3−]  EQN. 6

Substituting EQN. 6 into the reaction described above in EQN. 1, resultsin obtaining the dissolved CO2(aq) as a function of conductivity (L) asfollows:[CO2(aq)]=L ²/(K1*(A+B)²)  EQN. 7

In some embodiments, EQN. 7 is used by the control module to determinethe amount of CO2 to dissolve in H2O to obtain a desired conductivity.

The flow rate of carbon dioxide (FCO2) can be determined as follows:FCO2=FH2O*[CO2(aq)]  EQN. 8where FH2O is the flow rate of the water (H2O).

In some embodiments, all of the CO2 is dissolved in the H2O. In suchembodiments, a specific carbon dosage is determined as a function oftemperature as follows:[CO2(aq)]=L ² /f(T)  EQN. 9

Typically, conductivity (L) is set by the user. In various embodiments,the flow rate of the carbon dioxide (FCO2) is used by the control module125 for setting carbon dioxide mass flow controllers (CO2-MFC's). Insome embodiments, the FCO2 is used by the control module 125 for settingvalves and corresponding flow restrictors that the CO2 flows through. Inother embodiments, the FCO2 is used by the control module 125 forsetting valves and corresponding flow orifices that the CO2 flowsthrough.

The dissociation constant (K1) and the specific conductivity (L) can bedependent on the temperature of the water (H2O). The factor shown abovein EQN. 7, (K1*(A+B)²), can be expressed as a function of thetemperature of the water (H2O) as follows:(K1*(A+B)²)=f(T)  EQN. 10

In various embodiments, the temperature dependency of the factor,(K1*(A+B)²), is determined as follows using DI water controlled at totwo or more temperatures: for each temperature: 1) dissolve CO2 in DIwater, 2) measure a conductivity (L) of the DI-CO2, 3) take a sample ofthe DI-CO2, 4) heat or cool the sample to room temperature, 5) measurethe CO2(aq) concentration in the sample by titrating the sample with asolution of Sodium Hydroxide, and 6) for steps 3-5, isolate the samplefrom carbon dioxide in the air and isolate the air from carbon dioxidethat escapes from the sample.

In other embodiments, the temperature dependency of the factor,(K1*(A+B)²), is determined as follows using DI water controlled at twoor more temperatures: for each temperature: 1) dissolve CO2 in DI water,2) measure conductivity (L) and temperature (T) of the resulting DI-CO2,3) measure DI water flow rate and CO2 gas flow rate into the contactor,and 4) determine the CO2(aq) concentration by CO2 gas flow rate/DI waterflow rate. In some embodiments, the temperature dependence of(K1*(A+B)²) is stored in the control module and used for thedetermination of the CO2-flow into the contactor.

FIG. 2 shows another embodiment of system 101. System 101 can include aby-pass unit 130 in addition to contactor 115. By-pass unit 130 caninclude a plurality of valves and sensors to monitor and/or control theparameters of DI water passing through the unit. The valves and sensorscan be operated manually or controlled by the control module 125. Oneadvantage of by-pass unit 130 is that it allows for a high volume of DIwater to by-pass contactor 115 and mix with the DI-CO2 water beingreleased from contactor 115. Another advantage of by-pass unit 130 isthat it can shorten the response time required to go from highconductivity-low flow to low conductivity-high flow of the DI-CO2 waterand vice versa.

FIG. 3 shows another embodiment of system 101. The gases exiting the gasmodule can directly enter the contactor 115 or can be mixed with the DIwater prior to entering contactor 115. An advantage of this embodimentis that it can reduce the response time required to go from highconductivity-low flow to low conductivity-high flow of the DI-CO2 waterand vice versa.

FIG. 4 shows an exemplary embodiment of a device used to carbonateultra-pure DI water (i.e., add CO2 to the DI water). The device includesa gas module C1 in fluid communication with a contactor B1. The gasmodule C1 includes two inlets for gases, variable valves V51-V54, V58,and V59, and four mass flow controllers MFC 51-MFC54. Gas module C1 alsoincludes a feedback loop/mechanism where MFC52-MFC54 are mutuallyconnected via V57. In some embodiments, variable valves V51-54, V58, andV59 are on/off valves.

A feedback loop/mechanism can allow for correction of the parameters ofgases exiting gas module C1. For example, in the embodiment shown inFIG. 4, one or more of the MFCs may slightly degrade or deviate fromtheir initial flow rate calibration. To correct these deviations, afeedback loop can be included within the gas module C1 so as to updatecontrol mechanisms of the MFCs overtime.

The MFCs can be either adjusted manually or automatically. The MFCscontrol the gas flow to such an extent that most if not all of thecarbon dioxide entering B1 gets dissolved in the DI water and thereforethe resulting DI-CO2 water is “bubble free.” This prevents unevenconcentrations that may lead to poor cleaning properties. While FIG. 4illustrates a gas module with four MFCs, any number of MFC units can beutilized. In certain embodiments other flow controllers or concentrationmetering devices may be used in place of or in addition to the MFCs tocontrol the gas flow in gas module C1.

As shown in FIG. 4, DI water can enter the contactor B1 via V3 and gasesfrom gas module C1 can enter via V1 and V2. Light barriers or equivalentlevel sensors L3-L5 can be used to prevent gases from entering into theDI water line. In the contactor B1, carbon dioxide is mixed with the DIwater until a desired amount of CO2 concentration is achieved. TheDI-CO2 water is removed from B1 through an outlet DI-CO2 out via lightbarrier L3, sensor FR21 and valve V81. A sensor Q1 is connected inparallel to the DI-CO2 outlet. That is, a portion of the DI-CO2 waterfrom the contactor can travel through a drain line that includes thesensor Q1 and valves V89, V62, V80. The sensor module includes sensorsFR21 and Q1. Sensor FR21 monitors/controls the flow rate and sensor Q1monitors/controls the temperature and conductivity of the DI-CO2 water.The sensor Q1, valves V89, V62, and V80 together with valves V4, V61 andlevel sensor L5 form a control loop which allows for purging/venting ofthe contactor B1. Q1 and FR21 can also be in communication with the massflow controllers MFC51-MFC54 either directly or via a control moduleforming a feed-forward loop/mechanism.

The feed-forward mechanism allows the parameters of gases to be adjusted(for e.g., by changing the flow rate on one or more of the MFC) basedupon the measurements taken at the sensor Q1 and the sensor FR21 and adesired CO2 set point. Sensor Q1 typically contains a metal electrodewhich can be kept in direct contact with the water flowing through it.The information gathered in the sensor module is relayed to the controlmodule to adjust the amount of gases released from gas module C1. Thecontrol module can also allow for purging of the contactor B1. Incertain embodiments, the control module further controls the feedbackmechanism to adjust/correct deviations from initially calibrated valuesof the parameters set in gas module C1.

The feed-forward mechanism can control the CO2 concentration in theDI-CO2 water by monitoring parameters such as the temperature, flow rateand conductivity. For example, an operator of the device can use thecontrol module to enter/select in a computer/microprocessor, a desiredCO2 set point for the outflow concentration of CO2 or conductivity ofthe DI water. Higher concentrations of CO2 in the DI water call forutilization of greater CO2 flow rates into the contactor B1 and resultin a more acidic solution (e.g., pH of 4.5 or less); lowerconcentrations of CO2 in the DI water use a lower CO2 flow rate (lessCO2 gas) and result in a less acidic solution (e.g., pH of 4.6 orgreater). To control the output from the contactor B1, the system canutilizes the feed-forward mechanism in which the temperature, flow rateand conductivity values of the outflow are measured and electronicallysent to the control module for a determination of an input CO2concentration (e.g., flow rate) from the gas module C1.

In addition to controlling the gas module C1, the feed-forward mechanismcan also be involved in purging or venting the system. For example,during start up or when the CO2 set point is drastically changedresulting in a much lower input of CO2 from C1, a purge vent can beopened to vent excess gas (e.g., oxygen/air at start up and excess CO2at a set point change). In some embodiments, the purge vent is opened tovent excess gas when a conductivity set point of the DI-CO2 waterchanges from a high set point (e.g., above about 10 μS/cm) to a low setpoint (e.g., below about 95% of the high set point). When theconductivity set point of the DI-CO2 water is very high (e.g., greaterthan 40 μS/cm) a portion of dissolved non-CO2 gas strips from the DIwater inlet of the contactor into a gas phase of the contactor. To avoidstripping non-CO2 gas into the gas phase, in some embodiments, the purgevent is opened to vent excess CO2 gas when a conductivity set point ofthe DI-CO2 water is very high. Purging of the contactor B1 can becontrolled automatically through the control system. In variousembodiments the purge of the contactor B1 can be controlled manually bythe operator opening a purge vent.

FIG. 5 shows another exemplary embodiment of a device used to generateDI-CO2 water. In this embodiment, gas module C1 includes one gas inletin fluid communication with 4 variable valves V51-V54, 4 MFCsMFC51-MFC54 and two gas filters filter 50 and 51. As shown in FIG. 5,two separate loops can be formed containing two MFCs each and resultingin two separate gas outlets. Each of the two separate outlets candeliver the gas to the DI water prior to entering the contactor. Eachdelivery path can include a plurality of valves such as V1 a, V1 b, V2a, V2 b, V5 a and V5 b. Each delivery path can also include a pluralityof sensors such as M5 a, M5 b, and PR4. The sensors can be used tomonitor and/or control parameters such as flow rate or pressure of thegases passing through the system. In certain embodiments, one outlet candirect the gas into the DI-water before it enters the contactor and theother outlet can direct the gas into the contactor. An advantage ofmixing the CO2 gas and DI water prior to entering the contactor is ashorter response time to change from one conductivity of the DI-CO2water to another. Another advantage is the accuracy of the concentrationof CO2 in the DI-CO2 water and the conductivity of the DI-CO2 waterexiting the contactor. The two separate loops in the gas module C1provide an additional feedback mechanism to allow more control of theparameters of the gas entering and exiting the gas module C1.

FIG. 6 shows another exemplary embodiment of a device used to carbonateultra-pure DI water (i.e., add CO2 to the DI water). In this embodiment,gas module C1 includes two gas inlets that can be used for two separategases such as nitrogen and CO2. As shown in FIG. 6, variable valvesV52-V54, and MFCs MFC52-MFC54 are mutually connected to form a loop. Aseparate gas can enter the system via variable valve V51 and MFC51. Thetwo gases can be mixed in a desired proportion prior to exiting the gasmodule. Contactor B1 has an outlet that can release the gases via V4 andV61. The released gases can be recycled back into the gas module ifdesired or be released into the atmosphere.

FIG. 11 shows another exemplary embodiment of a device used to carbonateultra-pure DI water (i.e., add CO2 to the DI water). In this embodiment,variable valves V1 a, V1 b, V2 a, V2 b, V51, V52, V53 and V54 and flowrestrictors V51 a, V52 a, V53 a, and V54 a are used to control an amountof CO2 that is provided to an inlet of contactor B1. In some embodimentsthe amount of CO2 that is provided to the inlet is determined by thecontroller based on measured flow rate and temperature of the deionizedwater. In various embodiments, the amount of CO2 that is provided to theinlet is determined as described above in connection with EQN. 1 throughEQN. 10.

As shown in FIG. 11, DI water can enter the contactor B1 via V10 and CO2can enter the contactor B1 via V1 a, V2 a, V1 b, and V2 b. Level sensorL4 can be used to prevent gases from entering into the DI water line. Inthe contactor B1, CO2 is dissolved into the DI water until a desiredamount of CO2 concentration is achieved. The DI-CO2 water is removedfrom B1 through an outlet, DI-CO2 out, and through the process tools vialevel sensor L3, sensors TR1 and Q1 and valves V20, V21 and V22. SensorsTR1 and Q1 monitor temperature and conductivity, respectively, at theDI-CO2 outlet of the contactor B1. In some embodiments, the measuredtemperature and conductivity at the DI-CO2 outlet are provided to acontrol module that adjusts the valves that the CO2 flows through, thusadjusting an amount of CO2 that flows into the contactor B1.

Sensors FR21 and Q1 can be placed at the DI water inlet of the contactorB1 and also be in communication with the flow restrictors V51 a, V52 a,V53 a, and V54 a either directly or indirectly via a control module,forming a feed-forward loop/mechanism. Sensor FR21 monitors the flowrate of the DI water and sensor Q1 monitors the temperature andconductivity of the DI water. In various embodiment, sensor FR21 isplaced at the DI water inlet of the contactor B1 and sensor Q1 is placedat the DI-CO2 outlet of the contactor B1. In various embodiments, sensorFR21 is placed at the DI-CO2 outlet of the contactor B1 and sensor Q1 isplaced at the DI water inlet of the contactor B1 are located at anyposition within the system.

The valves V4 a and V4 b, flow restrictors V61 a V61 b, and V80,together with level sensor L5 form a control loop which allows forpurging and/or venting of the contactor B1 of a desired amount of CO2gas. In some embodiment, the purged and/or vented CO2 gas exits thesystem via a drain.

In some embodiments, a control module turns the variable valves V1 a, V1b, V2 a, V2 b, V51, V52, V53 and V54 on and off (e.g., pulse modulation)to achieve a desired average CO2 flow into the contactor B1 based on apressure measured at the CO2 inlet of the contactor B1 by pressuresensor PR4. In some embodiments, the desired average CO2 flow issubstantially equal to an amount of carbon dioxide determined by acontroller (e.g., control module 125, as shown above in FIG. 1). In someembodiments, the variable valves are turned on and off with a frequencythat is an input to the system. In some embodiments, the frequency isselected such that no fluctuation of the conductivity at the outletoccurs.

In some embodiments, the control module includes a pressure controllerto set a desired pressure of the CO2 at the inlet of the contactor B1.

In some embodiments, the control module selects a subset of the variablevalves V1 a, V1 b, V2 a, V2 b, V51, V52, V53 and V54 to turn on toachieve a desired CO2 flow into the contactor B1 based on a pressuremeasured at the inlet of the contactor B1 and a pressure drop across theflow restrictors (V51 a, V52 a, V53 a, and V54 a) that correspond to thevalves.

In some embodiments, a combination of pulse modulation, pressure controland selecting a subset of valves for an on state is used to control theflow of CO2 that is present at the inlet of the contactor B1.

In some embodiments, the deionized water provided by the deionized watersource and the carbon dioxide gas provided by the carbon dioxide sourceare mixed prior to entering the contactor.

Contactor B1 can have a by-pass unit B3 as shown in FIG. 6. By-pass unitB3 can include sensors LAH, L1 and LAL that can control and/or monitorparameters such as flow rate, pressure and liquid level. The sensors canbe in communication with the control module to allow for automaticcontrol or can be manually controlled. An advantage of the by-pass unitis when a high volume of the DI water is required. Another advantage ofthe by-pass unit is when a low concentration of CO2 in the DI water isdesired. Yet another advantage of the by-pass unit is the speed withwhich the conductivity of the DI-CO2 water can be changed from lowvolume-high conductivity to high volume-low conductivity and vice versa.

Apart from the by-pass unit B3, a high volume of DI water can also bedirected via a separate line passing through valve V31 and sensor FR31as shown in FIG. 6. This DI water can be mixed with the DI-CO2 waterexiting the contactor to alter the conductivity prior to exiting thesystem as desired.

A high volume of DI water in the range of about 20-80 L/min can beflowed through either the by-pass unit or the separate line or thecombination of the two. In some embodiments, the range of the highvolume of DI water can be about 32-50 L/min. In various embodiments,about 40-45 L/min of DI water can be flowed through the system.

The gas module is typically made of metals such as stainless steel. Thevalves, MFCs, and sensors are known to those skilled in the art and anycommercially available valves, MFCs and sensors, regulators or monitorscan be used. The gases and liquids typically pass through pipes ortubing made of corrosion resistant metals or metal alloys. Polymerictubing or pipes made from PTFE, PVDF, PFA, PVC, PP, PE, ECTFE, C-PVC,etc. can also be used wherever possible.

As shown in FIG. 7, the contactor is typically a vessel or a chamberthat can withstand high pressure. It can be made either of glass orquartz or metal or metal alloys such as stainless steel, brass orpolymers such as PTFE, PVDF, PFA, PVC, PP, PE, ECTFE, C-PVC, etc. Insome embodiments, the contactor is made from a combination of one ormore of the materials listed above.

A preferable contactor is shaped like a column and filled with “towerpacking” with a high surface area per volume. Fibers made of the abovementioned polymers can be used for the tower packing. The high surfacearea enhances the rate of mixing of the carbon dioxide and DI water.

The control module 125 can include stored data relating the input CO2flow rate from the gas module 110 to a specific temperature, DI-CO2water flow output, and conductivity as shown in FIGS. 8-10. FIG. 8 showsthe solubility of CO2 in DI water for different temperatures andpressures and FIG. 9 shows the specified conductivity range of 2-60μS/cm lead to a very wide gas dosage range. FIG. 10 shows thecorrelation between the conductivity of carbonated water at differenttemperatures. In certain embodiments, the control module 125 can verifythe desired input CO2 flow rate from the data stored therein and fromthe temperature, conductivity, flow rate, and set point valueselectronically sent or entered into the control module 125. In otherembodiments, the control module 125 can calculate/extrapolate the inputCO2 flow rate from the data stored therein in combination with thevalues electronically sent or entered. In certain embodiments, thecontrol module sends an electronic signal to automatically adjust gasmodule 110. In various embodiments, the values calculated by the controlmodule 125 can be used to manually adjust the parameters of gases and DIwater entering and/or exiting the system 101.

In the embodiment shown in FIG. 4, conductivity measurements at Q1 aretaken in a bypass line to a drain. In general, the measurements aretaken in a bypass line to the drain due to metal contamination from theelectrodes forming the conductivity sensor Q1. In other embodiments, itis possible to do a contamination free measurement in-line directly atthe DI-CO2 outlet. This may be done with special electrodes or a contactfree method.

In certain embodiments, an additional pressure regulator at the DI waterinlet can lead to additional stability in concentration and thusincrease the advantages for usage at a connected tool. A separation ofthe CO2 gas injection in two or more lines accordingly can beadvantageous in certain DI-CO2 water generation methods. For example, asmall amount of defined gas used to dilute the CO2 is preferable at lowconductivity to avoid conductivity fluctuation caused by bubbles at thegas inlet. In various embodiments, DI water flow measurement can also bedone at the water inlet.

In one embodiment, the gas control is achieved with mass-flowcontrollers. Due to a square relationship between the conductivity andconcentration as shown in FIG. 9, a control element with suchcharacteristics would be preferable. In another embodiment, a mechanismwith switched flow restrictors and controlled pressure or aconfiguration with PWM (pulse wide modulation) controlled valves can beemployed. For the range at very low conductivity, one option is toinject water which is already controlled enriched with CO2. FIG. 12 is aflow diagram of an embodiment of a method for generating DI-CO2 water.The method for generating DI-CO2 water includes supplying deionizedwater from a DI-CO2 source to a contactor (e.g., contactor 115, asdescribed above in FIG. 1) (Step 1210). The method for generating DI-CO2water also includes supplying CO2 from a CO2 source (e.g., gas module110, shown above in FIG. 1) to the contactor (Step 1215). In variousembodiments, the CO2 enters the contactor via a first inlet of thecontactor, and the DI-CO2 enters the contactor via a second inlet of thecontactor. In other embodiments, the CO2 and the DI-CO2 enter thecontactor via one inlet of the contactor.

The method also includes measuring a flow rate and a temperature of theDI water (Step 1220). Next, the method includes determining an amount ofCO2 to supply to the contactor such that a specific conductivity ofDI-CO2 water is generator by the contactor (Step 1225). In someembodiments, the amount of CO2 to supply to the contactor is determinedbased on the measured flow rate and temperature of the DI water. In someembodiments, the amount of CO2 to supply to the contactor is determinedaccording to EQNS. 1-10, as described above. In general, the amount ofCO2 to supply to the contactor is determined based on a desiredconductivity of the DI-CO2. In some embodiments, the desiredconductivity is set by a user and the amount of CO2 to supply to thecontractor is controlled by a controller (e.g., controller 125). In someembodiments, the amount of CO2 to supply to the contactor is based on adesired pressure of CO2 at an inlet of the contactor. In certainembodiments, the contactor is in communication with one or more sensorsthat measure the flow rate and temperature.

The method illustrated in FIG. 12 also includes supplying the determinedamount of CO2 to the contactor via one or more valves (e.g., variablevalves V1 a, V1 b, V2 a, V2 b, V51, V52, V53 and V54, as described abovein FIG. 11) that are in communication with the supply of CO2 and thecontactor (Step 1230). In some embodiments, the flow rate of the one ormore valves is modified with one or more flow restrictors (e.g., flowrestrictors V51 a, V52 a, V53 a, and V54 a, as described above in FIG.11) and/or one or more flow orifices. In some embodiments, supplying thedetermined amount of CO2 involves varying one or more valves between anopen and a closed position such that an average amount of CO2 flows fromthe CO2 source to the contactor. In some embodiments, the average amountof CO2 is substantially equal to the amount of CO2 determined above inStep 1225.

The DI-CO2 water generated by the present invention provides a damagefree process for cleaning semiconductor devices in an electrically inertatmosphere. The dissolved CO2 reduces the resistivity of the DI water toa level that prevents surface charging. It also acidifies the DI waterand increases the zeta potential. The DI-CO2 water allows to protect theintegrity of fragile semiconductor devices. For example, the DI-CO2water can be used to dissolve, oxidize, etch, and scrub contaminantsfrom the surface of silicon wafers. The DI-CO2 water also preventscorrosion of metals during the wet-cleaning steps. The DI-CO2 water canalso be used in commercially available wet cleaning devices or tools asa component or as a separate delivery system. Variations, modifications,and other implementations of what is described herein will occur tothose of ordinary skill in the art without departing from the spirit andthe scope of the invention. Accordingly, the invention is not to belimited only to the preceding illustrative descriptions.

What is claimed is:
 1. A method for carbonation of deionized watercomprising: supplying deionized water to a contactor; supplying carbondioxide gas to the contactor; measuring, with at least one sensor, flowrate of the deionized water and temperature of the deionized water,wherein the at least one sensor is positioned at an inlet of thecontactor or an outlet of the contactor; determining an amount of carbondioxide gas to supply to the contactor such that a specific conductivityof carbonated deionized water is generated by the contactor incommunication with the at least one sensor and the supply of carbondioxide gas, wherein the determination is based on the measured flowrate and temperature; supplying the determined amount of carbon dioxideto the contactor via one or more flow restrictors and one or more valvesthat are in fluid communication with the supply of carbon dioxide gasand the contactor; and flowing the carbonated deionized water of aspecific conductivity from the contactor.
 2. The method of claim 1further comprising varying the one or more valves between an open and aclosed position such that an average amount of carbon dioxide gas thatflows from the carbon dioxide gas source to the contactor issubstantially equal to the determined amount of carbon dioxide gassupplied by the carbon dioxide gas source.
 3. The method of claim 1further comprising purging an amount of the carbon dioxide gas throughan outlet of the contactor.
 4. The method of claim 3 further comprisingdetermining the amount of carbon dioxide gas to purge such that aspecific conductivity of the carbonated deionized water is generated inthe contactor.
 5. The method of claim 3 further comprising at least oneflow restrictor in fluid communication with the outlet of the contactorand a drain for controlling the amount and flow rate of carbon dioxidegas purged from the contactor.
 6. The method of claim 3 furthercomprising at least one flow orifice in fluid communication with theoutlet of the contactor and a drain for controlling the amount and flowrate of carbon dioxide gas purged from the contactor.
 7. The method ofclaim 1 further comprising setting a pressure of carbon dioxide gas atthe at least one inlet.
 8. The method of claim 1 further comprisingmixing deionized water provided by the deionized water source and carbondioxide provided by the carbon dioxide source prior to entering thecontactor.
 9. The method of claim 1 further comprising: measuring flowrate, with a first sensor, of the deionized water at an inlet of thecontactor; and measuring temperature, with a second sensor, of thedeionized water at an outlet of the contactor.
 10. The method of claim 1further comprising: measuring temperature, with a first sensor, of thedeionized water at an inlet of the contactor; and measuring flow rate,with a second sensor, of the deionized water at an outlet of thecontactor.